1. Field of the Invention
This invention relates generally to a record disc player for reproducing audio, video or other information signals on a rotated disc by means of a pick-up carried by an arm for tracing or tracking the path or groove in which the signals are recorded, and the invention is more particularly directed to an improved drive apparatus for effecting movements of the pick-up arm.
2. Description of the Prior Art
It is known to provide a record disc player with a so-called linear tracking pick-up arm which is mounted so that the stylus of the pick-up at the free end of the arm will move substantially along a radius of the record disc when tracking or tracing a spiral record groove on the latter. In order to achieve such linear tracking, the end of the pick-up arm remote from the pick-up or cartridge is mounted for movement along a straight guide shaft which is substantially parallel to a radius of the record disc and from which the pick-up arm extends substantially at right angles to the axis of the guide shaft. During the playing or reproducing of the recorded signal, that is, when the record groove is being traced, the arm is driven along the guide shaft at a relatively slow speed, which is normally 0.05 mm/sec. On the other hand, during lead-in, that is, when the pick-up or cartridge is being moved from its rest position to an initial position where its stylus first engages the record groove adjacent the outer periphery of the record disc, and also during return, that is, when the pick-up is moved back to its rest position after completion of the playing or reproducing of all of the recorded signals, the arm is driven at a high speed which is normally 100 mm/sec. It will be seen that the speed at which the arm is driven during lead-in and return is about 2000 times the speed at which the arm is driven during actual playing or reproducing. Such great difference in the speeds at which the arm must be driven during playing or reproducing and during lead-in and return, respectively, leads to substantial problems. More particularly, if the arm is to be driven by a single motor, as in a conventional apparatus, it is not possible to provide the motor with a speed servo control circuit having an effective range large enough to encompass the desired drive speeds for playing and for lead-in and return, respectively. Therefore, in the case of an existing linear tracking arm drive apparatus employing a single motor, the drive speed of the arm during lead-in and return is substantially required, that is, is substantially less than 100 mm/sec., so that the time required for an operating cycle of the record disc player is undesirably increased thereby.
In another proposed linear tracking arm drive apparatus, the rotational torque of the motor for driving the arm along the guide shaft is applied through a magnetic clutch and, during the playing or reproducing operation, an electromagnetic brake is suitably controlled to reduce the speed of movement of the arm while causing slipping of the magnetic clutch. However, in such arrangement, variations occur in the arm drive speed and the drive torque so that there is an undesirable lack of stability in the driving of the arm during playback or reproducing with the result that the tone quality of the reproduced sound is degraded.